Referring to FIG. 9 showing a conventional clutch cover assembly, flywheel 11 driven by an engine (not shown) is concentrically fixed to an outer peripheral portion of a clutch cover body 12 of a dish-like form having a central aperture of large diameter.
The flywheel 11 and the clutch cover body 12 form an internal space 20, in which a clutch disk 13 is concentrically disposed and is connected to an output shaft (not shown). A pressure plate 14 for pressing the clutch disk 13 toward the flywheel 11 is concentrically disposed in the internal space 20 between the disk 13 and the clutch cover body 12.
A diaphragm spring 16 which is formed by an annular metal member is used for pressing the clutch disk 13 onto the flywheel 11 by the pressure plate 14.
The diaphragm spring 16 is integrally provided at the radially outer portion with an annular spring portion 16a, and is integrally provided at the radially inner portion with many radial tongues 5 extending radially inwardly from the inner periphery of said annular spring portion 16a. These tongues 5 form slits 15 therebetween. The openings 18 are formed radially outside the slits 15.
A pair of metal wire rings 17 having the same radii are pinched on opposite surfaces of the diaphragm spring 16 by pins 19 fitted in the openings 18, respectively.
At the side of the diaphragm spring 16 opposite to the flywheel 11 is disposed a release bearing, which is slidable along the output shaft and is connected through a link mechanism (not shown) to a clutch pedal, so that it may push the tongues 5 of the diaphragm spring 16 toward the flywheel 11.
In the above structures, when the clutch is engaged, the diaphragm spring 16 elastically presses the pressure plate 14 toward the flywheel 11 using the wire rings 17 as the fulcrum, so that the clutch disk 13 is pressed onto the flywheel 11 by the pressure plate 14. Thus, the rotational force of the flywheel 11 is transmitted to the clutch disk 13.
However, in the above structures, the flywheel 11 and the clutch disk 13 as well as the clutch disk 13 and the pressure plate 14 frequently slide on each other causing friction heat. They do not have a cooling function, so that the heat generated in the clutch disk 13 causes rapid wear of the clutch disk 13, and, in severe use condition, causes thermal damage to the friction member and curvature of the pressure plate 14.
In order to cool the friction parts, structures, such as shown in FIG. 10 have been proposed, in which edges of the tongues 5 of the diaphragm spring 16 are bent, e.g., by press machining, in opposite directions to form vane-like shape for supplying air into the internal space through the slits 15 as shown by arrows A when the diaphragm spring 16 rotates in the direction X. However, large-scale equipment is required for forming the tongues 5 of such shape and results in high cost. Further, the modified shape of the tongues alone can not attain good flowing condition of the air in the internal space 20, and thus, can not sufficiently perform the cooling function. The object of the invention is to overcome these problems.